1. Field of the Invention
This invention relates generally to footwear and, more specifically, without limitation, to an outsole for footwear.
2. Description of the Related Art
Various man-made products are generally imposed between a user's feet and supporting surfaces situated therebeneath. Such man-made products should generally be designed to provide support and shock attenuation to provide protection for, including prevent structural injury to, the user's feet. In addition, some of such man-made products are also designed to provide improved appearance, convenience, endurance, etc. Unfortunately, such man-made products tend to be detrimental to the human musculoskeletal structures.
As disclosed in U.S. Pat. No. 4,272,899, issued Jun. 16, 1981 to Jeffrey S. Brooks, the disclosures and teachings of which are incorporated herein by reference, a contoured insole structure may be provided in shoes to reduce abnormal stress from the heel to the metatarsals by properly supporting and stabilizing the feet during development thereof. By so doing, the associated stresses placed upon the medial column of the foot is also reduced, distributing the body weight more evenly on the sole of the foot.
More specifically, when walking or running, the lateral (outside) portion of the human heel is generally the first part of the foot to strike the ground, with the foot then pivoting on the heel to bring the lateral part of the forefoot into a position whereat it bears against an underlying surface. At that point, the foot resides in a supinated (inclined upwardly from the lateral to the medial side of the foot). The foot then pronates until all of the metatarsal heads are in a substantially horizontal planar orientation relative to the underlying supporting surface (assuming the supporting surface is substantially horizontal) and the heel, ideally, is oriented perpendicularly to that underlying surface. The foot is then in a neutral position with the subtalar joint thereof, neither pronated nor supinated. The bone structural alignment should be firmly supported when the foot assumes such neutral position in order to prevent the ligaments, muscles and tendons of the foot from becoming over-stressed.
Various skeletal characteristics of the feet that are pertinent to proper foot support include the first, second, third, fourth and fifth metatarsal heads, indicated in phantom at M1 through M5 in FIG. 1; first, second, third, fourth and fifth metatarsal necks associated with the respective metatarsal heads M1-M5, indicated in phantom at N1 through N5; first, second, third, fourth and fifth proximal phalanges spaced distally from the respective metatarsal heads M1-M5, indicated in phantom at P1 through P5; and first, second, third, fourth and fifth metatarsal phalangeal joints spaced between the respective metatarsal heads M1-M5 and proximal phalanges P1-P5, indicated at J1 through J5 in FIG. 1. Further, various muscles and tendons characteristically interact to stabilize the foot during the sequence of progressive movements normally experienced in a walking or running gait in preparation for movement from the neutral position to a propulsive phase of the gait cycle, sometimes referred to as "toe-off" or "push-off".
Thus, the progressive phases of gait are heel strike, when the heel hits the ground; midstance, when stability of the arch is an essential necessity; and propulsive phase, as the heel lifts off the ground and the body weight shifts onto the ball of the foot. During the transition from the neutral position through toe-off, it is preferable that the second and third metatarsals be firmly supported, and that the first metatarsal head plantarflex (move downward) relative the second and third metatarsal heads. The toes also should generally be firmly supported during toe-off so that they remain straight, and thus stronger, promoting a "pillar effect" by the phalanges.
Flexion of the first metatarsal phalangeal joint (i.e., the great toe joint) is normally approximately fifteen degrees to the associated metatarsal in a dorsiflexed position when standing, and increases to between sixty-five and ninety degrees, depending on the available motion and the activity required by the joint just prior to lifting off the underlying supporting surface. Proper foot care requires that the relationship among the foot bones comprising the metatarsophalangeal joints be maintained during flexure of the foot during walking, running, etc. A study of the normal length pattern of metatarsal bones at the metatarsophalangeal joints, based on 279 radiographs and reported in Clinical Foot Roentgenology, by Gamble & Yale, Williams & Wilkins Publishers, Baltimore, 1966, disclosed that the relative spacing of those joints approximate an arcuate relationship that may be generally described as a parabolic curve, as suggested by the dashed line designated by "A" in FIG. 1.
In an ideal foot posture situation for minimal stress, the position in which the feet, as weight-bearing organs, would normally realize greatest efficiency (including an optimal ratio of supination and pronation) is one in which the subtalar joint is approximately forty-two degrees from the transverse plane, approximately sixteen degrees from the saggital plane, and approximately forty-eight degrees from the frontal plane, sometimes referred to as the neutral position hereinbefore mentioned. In the neutral position, the leg and calcaneus are perpendicular to the weight bearing surface, and the knee joint, ankle joint and forefoot, including the plane of the metatarsal heads, are substantially parallel to the subtalar joint and to the walking surface.
In view of the foregoing, it should be obvious that the user's feet should be placed in their individually most efficient position to function properly and to reduce excessive strain not only on the feet but also on the lower body structure supported by the feet, that certain parts of the feet are generally subjected to higher stresses during standing, running and walking, and that other parts of the feet require different degrees of support for maximum biomechanical efficiency, particularly since high impact forces to the foot are generally transferred to other skeletal structures, such as the shins, knees, and lower back region. Control of the user's foot must begin in the heel and progressively proceed to the more distally situated parts of the foot, including providing stability of the forefoot and proper flexure of the metatarsophalangeal joints, in order for the foot to function properly through the normal phases of gait.
As the thickness of the outsole of a shoe is increased, the inability of the shoe to allow appropriate arcuate flexure at the metatarsal joints of the wearer's foot confined to thick-soled footwear becomes more pronounced. For example, such thick-soled footwear may arise from platform-type outsoles utilized on selected footwear to enhance the wearer's apparent height, on a corrective shoe to compensate for the difference in length of the wearer's legs, etc.
Because of the inability of platform- or thick-soled shoes to allow such appropriate flexure, the normal functions of the wearer's foot--and the resulting increased stresses and strains on the wearer's musculo-skeletal structure--may also be substantially pronounced. In that event, proficiency of a wearer's foot may be greatly reduced in footwear utilizing platform- or thick-soled footwear.
Thus, what is needed is an outsole for footwear which, even when having a platform-type structure, provides appropriate flexure at the metatarsophalangeal joints, an appropriate amount of support and shock attenuation for different regions of the foot to thereby provide a proper environment that promotes a balanced foot position for healthy postural and skeletal structural support thus allowing the parts of the foot to function in a way which provides maximum efficiency, to prepare the body for stresses normally subjected thereto, and to protect those parts of the foot which are subjected to high impact forces.